Information about E-Mail good app in iphone

Hello everyone!
since i got my new iPhone i'm still looking for decent apps. Currently for a good E-Mail app.

Outlook and Spark are my favorites so far, but it's useless to have 2 E-Mail apps , well.. 3 if we count the Apple mail app.
Outlook had some security issues earlier this year, but i didnt find anthing from the last months about it.
I like it so far and is over Spark when it comes to my favorites.

But, still a bit scared about the issue they had.
What do you guys think? Safe to use?
Thank's a lot!